1. Field of the Invention
The present invention relates generally to utility knives and more specifically to a spring loaded utility knife wherein the blade is constantly biased toward a retracted position so that upon the removal of manual pressure holding the blade in an exposed cutting position, the blade is automatically retracted to a non-exposed position under the bias of the spring.
2. Discussion of the Related Art
A number of utility knives have been proposed which have blade is arranged within a housing and arranged to project by an amount suitable for cutting paper, tape and the like. While these type of knives have found considerable utility, there has been a problem that the blade does not automatically retract upon the cutting operation being completed and requires that the operator take steps to have the blade move back within the housing of the device. One such device is disclosed in U.S. Pat. No. 5,813,121 issued on Sep. 29, 1998 in the name of Gringer. This device is such as to feature a side mounted slider which projects out of one side of the handle or housing and includes a series of positions in which the blade can be locked in a projected state. Due to the arrangement of the thumb piece being located on one side of the housing, this arrangement is limited to use by right handed people. Further, in the embodiments wherein a serpentine spring is used to retract the blade upon a lock mechanism is released, the spring, the blade carrier, the lock mechanism and the thumb piece are all integrally formed. The molding process required to achieve the production of this element is, of course, complex adding to the production cost. It further prevents the position/orientation of the blade carrier within the handle or housing from being varied to permit the use of differently shaped cutting blades and limits the degree to which the amount of projection of each blade can be adjusted in accordance with the task in hand.
U.S. Pat. No. 5,581,890 issued on Dec. 10, 1997 in the name of Schmidt, discloses a utility knife which permits the blade to be retracted back into the housing automatically upon the removal of manually applied pressure on a thumb piece. Nevertheless, this arrangement is provided with a rack on the interior of the housing and a projection on the blade carrier which is adapted to engage the rack in a kind of ratchet type of arrangement. This of course inhibits the change of the blade carrier orientation within the housing and thus prevents the use of a variety of different types of blades in the same device.
A further drawback that both of the above arrangements suffer from is the manner in which the two halves of the handles interconnect with one another. While the arrangement in U.S. Pat. No. 5,813,121 attempts to render the halves readily disengageable from one another via the provision of a latch member which is mounted on a flexible portion and arranged to bent via the application of a digit such as the operator's thumb, the arrangement tends to be relative fragile and apt to fail after a large number of operations. The arrangement disclosed in U.S. Pat. No. 5,581,890, on the other hand, is such as to use a barbed member which snaps into a locking position once inserted sufficiently through an aperture formed in the other half. In this arrangement the ability to separate the two halves has not been given much consideration tends to be difficult to separate once they are engaged with one another.
Accordingly, there exists a need for a utility knife which is readily separable into its two halves, which has an engaging mechanism which is robust and which is not apt to fail after a relatively small number of operations, and which allows for a variety of different blades to be mounted and used in accordance with the desires of the user.